If I understand completely, what you want to do is create a Freeze Frame, from the last Frame of each Video Clip and then place that into the "gap," while the Audio completes. The Camera icon will do a Frame Capture when that Clip is Selected and the CTI (Current Time Indicator w/ red Edit Line) is placed over the last Frame. You then just drag that still image from the Project Panel and place it in the gap, extending it for whatever Duration you need.